Cellulosic product and process for its production

ABSTRACT

The present invention relates to a process for the production of a cellulosic product which comprises (i) providing an aqueous cellulosic suspension; (ii) adding to the suspension a clay having 3R 2  stacking; and (iii) dewatering the obtained suspension. The invention also relates to a process for the production of a cellulosic product which comprises (i) providing an aqueous cellulosic suspension; (ii) adding to the suspension a cationic clay; (iii) adding to the suspension one or more drainage and retention aids comprising at least one cationic polymer; and (iv) dewatering the obtained suspension. The invention further relates to a cellulosic product comprising clay having 3R 2  stacking.

This application claims priority based on U.S. Provisional PatentApplication No. 60/427,618, filed Nov. 19, 2002

The present invention relates to a process for the production of acellulosic product which comprises treating cellulosic fibres with clayhaving 3R₂ stacking, and to a process for the production of a cellulosicproduct which comprises treating cellulosic fibres with cationic clay.The invention also relates to a cellulosic product comprising clayhaving 3R₂ stacking.

BACKGROUND OF THE INVENTION

Pulp suspensions are widely used for making cellulosic products such as,for example, pulp and paper, and contain, apart from cellulosic fibres,also compounds which have a negative impact on the production process.Such compounds are found both in cellulosic suspensions originating fromvirgin pulp and from recycled pulp.

In virgin pulp suspensions such disturbing/detrimental substances areprimarily hemicellulose, lignin as well as lipophilic and hydrophilicextractives. Apart from the cellulose, these substances are to a varyingextent dissolved or colloidally dispersed into the process waters duringthe pulping and bleaching operations. Compounds which are releasedduring pulping and bleaching operations are commonly referred to aspitch. Examples of pitch include wood resins such as lipophilicextractives (fatty and resin acids, sterols, stearyl esters,triglycerides), and also fats, terpenes, terpeniods, waxes, etc.

In recycled pulp suspensions the compounds having a negative influenceon the paper making process mainly consist of glues, hot-melt plasticsinks and latex, just to mention a few compounds—which are commonlyreferred to as stickies. Apart from pitch and stickies the suspensionalso contains charged contaminants like salts and various wood polymersof which the charged, low charged or non-charged compounds compete withthe cellulose with respect to the adsorption and interaction with addedperformance chemicals such as drainage and retention aids, sizingagents, etc. Usually such disturbing compounds are referred to asanionic trash.

All of the above-mentioned compounds interfere with the pulp and papermaking processes in various ways. For instance, some of them precipitatedue to changes in the properties of the pulp suspension and areeventually deposited on various mechanical parts of the paper machinesuch as, for example, screens and felts. Over time, the deposits willlead to breakdowns on the paper machine often in form of breaking of thepaper web, whereby the paper machine has to be stopped for cleaning.Furthermore, paper mills tend to re-circulate the white water to agreater extent than previously, which increases the presence ofdisturbing and detrimental substances in the suspension.

Various additives have been used in order to decrease the negativeimpact of the above-mentioned detrimental/disturbing substances. Forexample, talc has been widely used for adsorbing pitch and stickies.Also various types of clays have been employed for reducing the impactof detrimental compounds.

Japanese laid-open patent application No. 1985-94687 relates to apitch-adsorbing agent containing hydrotalcite.

SUMMARY OF THE INVENTION

The present invention is generally directed to a process in whichcellulosic fibres are treated with a clay having 3R₂ stacking. Thepresent invention is also generally directed to a process in whichcellulosic fibres are treated with a cationic clay. Furthermore, theinvention is directed to a process for the production of a cellulosicproduct which comprises adding a clay having 3R₂ stacking to an aqueoussuspension containing cellulosic fibres. The present invention isfurther generally directed to a cellulosic product comprising a clayhaving 3R₂ stacking.

The present invention further relates to a process for the production ofa cellulosic product which comprises (i) providing an aqueous suspensioncontaining cellulosic fibres; (ii) adding to the suspension a clayhaving 3R₂ stacking and optionally one or more drainage (dewatering) andretention aids; and (iii) dewatering the obtained suspension. Theinvention further relates to a process for the production of acellulosic product which comprises (i) providing an aqueous suspensioncontaining cellulosic fibres; (ii) adding to the suspension cationicclay; (iii) adding to the suspension one or more drainage (dewatering)and retention aids comprising at least one cationic polymer; and (iv)dewatering the obtained suspension. The cellulosic product produced ispreferably pulp and/or paper.

DETAILED DESCRIPTION OF THE INVENTION

It has surprisingly been found that the negative impact on pulp andpaper making processes by the presence of disturbing and detrimentalsubstances in aqueous cellulosic pulp suspensions, specifically problemscaused by pitch and stickies, can be reduced by treating cellulosicfibres with a clay according to the invention.

It has surprisingly also been found that the addition to cellulosicsuspensions of a clay according to the invention, specifically acationic and/or 3R₂ clay, in conjunction with additives used for pulpand paper making not only allows for adsorption and removal ofdisturbing substances, but it also improves the performance of theadditives used in the process, as compared to the situation when theclay is not added. Examples of such additives for which improvedperformance is observed include retention and dewatering aids, sizingagents, etc. preferably, the clay is used together with one or moredrainage and retention aids comprising at least one cationic polymer.Thus, the present invention provides improved drainage (dewatering) andretention in pulp and paper making processes as well as improved sizingin paper making processes, while simultaneously further reducing thecontent of disturbing and detrimental substances in the cellulosicsuspension.

The clay according to the invention can be derived from naturallyoccurring clays, chemically and/or physically modified naturallyoccurring clays, and synthetic clays. Naturally occurring clays normallyhave an essentially crystalline structure. However, syntheticallyobtained clays may also additionally contain amorphous material havingessentially the same chemical composition as the crystalline structures.The amount of amorphous material present in synthetic clay dependsmainly on the reaction parameters used. The term “clay”, as used herein,refers to clays having essentially crystalline structure and also toclays containing both crystalline and amorphous structures.

Clays are characterised by a layered structure wherein atoms within thelayers (lamellae) are cross-linked by chemical bonds, while the atoms ofadjacent layers interact mainly by physical forces. The layers of theclay may be non-charged or charged depending on the type of atomspresent in the layers. If the layers are charged, then the space betweenthese layers, also designated as the interlayer space, contains ionswhich have the opposite charge with respect to the charge of the layers.The term “cationic clay”, as used herein, refers to clays havingpositively charged layers and anions present in the interlayer space.The term “anionic clay”, as used herein, refers to clays havingnegatively charged layers and cations present in the interlayer space.Usually the ions in the interlayer space are exchangeable.

The clays according to the invention can virtually have any anion,optionally also water molecules, present in the interlayer space.Examples of common anions that can be present in the interlayer spaceinclude NO₃ ^(−a), OH⁻, Cl⁻, Br⁻, I⁻, CO₃ ²⁻, SO₄ ²⁻, SiO₃ ²⁻, CrO₄ ²⁻;BO₃ ²⁻, MnO₄—, HGaO₃ ², HVO₄ ⁻, and ClO⁴⁻, as well as pillaring orintercalating anions such as V₁₀O₂₈ ⁶⁻ and MO₇O₂₄ ⁶⁻, mono-carboxylateslike acetate, dicarboxylates such as oxalate, and alkyl sulphonates suchas lauryl sulphonate; usually hydroxide and carbonate. Naturallyoccurring clays of the invention commonly have carbonate anions in theinterlayer space.

The layer or lamella of the clay suitably comprises at least twodifferent metal atoms having different valences. Suitably, one metalatom is divalent and the other metal atom is suitably trivalent.However, the layer may also comprise more than two metal atoms. Thecharge of the layer is governed by the ratio of metal atoms havingdifferent valences. For instance, a higher amount of trivalent metalswill render a layer having an increased density of the positive charge.Suitably, the clay of the invention comprises layers containing divalentand trivalent metals in a ratio so that the overall charge of the layersis cationic, and the interlayers comprise anions. Preferably, the layersessentially consist of divalent and trivalent metals in such a ratiothat the overall charge of the layers is cationic.

Synthetically produced and naturally occurring clays according to theinvention can be characterised by the general formula:[M_(m) ²⁺M_(n) ³⁺(OH)_(2m+2n)]X_(n/z) ^(Z−) .bH₂O,wherein m and n, independently of each other, are integers having avalue such that m/n is in the range of from 1 to 10, preferably 1 to 6,more preferably 2 to 4 and most preferably values around 3; b is aninteger having a value in the range of from 0 to 10, suitably a valuefrom 2 to 6, and often a value about 4; X_(n/z) ^(Z−) is an anion wherez is an integer from 1 to 10, preferably from 1 to 6, suitable X_(n/z)^(Z−) including NO₃ ⁻, OH⁻, Cl⁻, Br⁻, I⁻, CO₃ ²⁻, SO₄ ²⁻, SiO₃ ²⁻, CrO₄²⁻, BO₃ ²⁻, MnO₄ ⁻, HGaO₃ ²⁻, HVO₄ ⁻, ClO₄ ⁻, pillaring andintercalating anions such as V₁₀O₂₈ ⁶⁻ and MO₇O₂₄ ⁶⁻, mono-carboxylateslike acetate, dicarboxylates such as oxalate, and alkyl sulphonates suchas lauryl sulphonate; M²⁺ is a divalent metal atom, suitable divalentmetal atoms including Be, Mg, Cu, Ni, Co, Zn, Fe, Mn, Cd, and Ca,preferably Mg; M³⁺ is a trivalent metal atom, suitable trivalent metalatoms including Al, Ga, Ni, Co, Fe, Mn, Cr, V, Ti and In, preferably Al.Preferably, the divalent metal is magnesium and the trivalent metal isaluminum, rendering the general formula:[M_(m) ²⁺M_(n) ³⁺(OH)_(2m+2n)]X_(n/z) ^(Z−) .bH₂O.

According to one preferred embodiment of the invention, the clay iscationic. Examples of suitable cationic clays according to the inventioninclude hydrotalcite, manasseite, pyroaurite, sjögrenite, stichtite,barbertonite, takovite, reevesite, desautelsite, motukoreaite,wermiandite, meixnerite, coalingite, chloromagalumite, carrboydite,honessite, woodwardite, iowaite, hydrohonessite, mountkeithite, etc.Examples of terms also used to describe these clays includehydrotalcite-like compounds and layered double hydroxide compounds.

According to another preferred embodiment of the invention, the clay hasa specific stacking, namely a 3R₂ stacking; this type of clay is hereinalso referred to as “3R₂ clay”. The 3R₂ clay is preferably cationic, andthe clay can be any of those mentioned above. Preferably, the clay ismagnesium-aluminum-containing 3R₂ clay. The 3R₂ clay suitably has athree-layer repeat. The 3R₂ stacking polytype of clay has a differentlayer arrangement/stacking than the 3R₁ stacking polytype, herein alsoreferred to as “3R₁ clay”. The 3R₁ and 3R₂ clays can be distinguishedfrom each other by X-ray diffraction/reflections patterns by theintensities of the 107 and 108 d_(hkl) reflections. The 3R₂ clay has astronger d_(hkl) 107 reflection close to 45° 2 theta (according to Dritsand Bookin), whereas the 3R₁ clay has a stronger d_(hkl) reflectionclose to 47° 2 theta (the d_(hkl) 108 reflection). The presence of peaksat both 45° 2 theta and 47° 2 theta indicates the presence of a mixtureof 3R₁ and 3R₂ clays. It is understood that the precise 2 theta valuesfor the 107 and 108 d_(hkl) reflections will depend on the lattice “a”and “c” structural parameters for the clay, for example Mg—Al clay. Ofcourse, there are some other differences in the X-ray diffractionpatterns as well, but it is believed that this is the best range of thed_(hkl) reflections to make such a distinction. Furthermore, the clayhaving 3R₂ stacking has a different morphology compared to that ofconventional 3R₁ clays, as can be detected by the SEM examinations. The3R₂ clay appears to have a structure with irregular flake-like plateletswhich are randomly agglomerated, whereas the conventional and prior art3R₁ clays have regular well-formed layers of platelets which arearranged in the usual book-stack form.

Clays having 3R₂ stacking according to the invention can be prepared byhydrothermal treatment (solvo thermal) of a slurry containing analuminium source and a magnesium source. Examples of suitable clayshaving 3R₂ stacking, e.g. Mg—Al clays, according to the invention andmethods for their preparation include those disclosed in InternationalPatent Application Publication No. WO 01/12550, the disclosure of whichis hereby incorporated herein by reference.

According to one preferred embodiment of the invention, the clay having3R₂ stacking is added to an aqueous suspension containing cellulosicfibres in a process for the production of a cellulosic product like pulpand paper. It has been observed that if the 3R₂ clay is added to such asuspension, improved removal of disturbing substances such as pitch andstickies is achieved over the addition of conventional clay having 3R₁stacking.

The clay is suitably mixed with cellulosic fibres by being added to anaqueous suspension containing cellulosic fibres (herein also referred toas “aqueous cellulosic suspension” and “cellulosic suspension”) eitheras a slurry (suspension) or powder, which can be easily dispersed inwater. The suspension or powder of clay may further also contain othercomponents such as, for example, dispersing and/or protecting agents,which can contribute to the overall effect of the clay. Such agents canhave non-ionic, anionic or cationic character. Examples of suitableprotective agents or colloids include water-soluble cellulosederivatives, e.g. hydroxyethyl- and hydroxypropyl-, methylhydroxypropyl-and ethyl-hydroxyethyl-cellulose, methyl- and carboxymethylcellulose,gelatine, starch, guar gum, xanthan gum, polyvinyl alcohol, etc.Examples of suitable dispersing agents include, non-ionic agents, e.g.ethoxytated fatty acids, fatty acids, alkyl phenols or fatty acidamides, ethoxylated and non-ethoxylated glycerol esters, sorbitan estersof fatty acids, non-ionic surfactants, polyols and/or their derivatives;anionic agents, e.g. as alkyl or alkylaryl sulphates, sulphonates,ethersulphonates, polyacrylic acid; and cationic agent, e.g. esterquatsobtained by reacting alkanolamines with mixtures of fatty acids anddicarboxylic acids, optionally alkoxylating the resulting esters andquatemising the products, quatemised fatty acid amides, betaines,dimethyl dialkyl or dialkylaryl ammonium salts, and cationic geminidispersing agents.

The clay can be added at any point in the cellulosic product productionprocess starting from the point where wood chips are disintegrated up tothe point in the process where dewatering of the cellulosic suspensiontakes place. The cellulosic product can be in any form such as, forexample, in the form of a web or sheet, e.g. pulp sheets and papersheets.

According to a preferred embodiment of the invention, the clay is addedto a cellulosic suspension of a pulp making process. The clay can beadded prior to or after the pulping process which can be kraft,mechanical, thermo-mechanical, chemomechanical, chemo-thermo-mechanicalpulping processes. The clay can be added just before the pulping processor directly to the pulping process, such as to the digester. However, itis preferred that the clay is added to the cellulosic suspensionsubsequent to chemical digestion such as after the brown stock washer,or after refining of (chemo-)mechanical pulp. Usually, the cellulosicpulp is bleached in a multi stage bleaching process comprising differentbleaching stages and the clay can be added to any bleaching sequence.Examples of suitable bleaching stages include chlorine bleaching stages,e.g. elementary chlorine and chlorine dioxide bleaching stages,non-chlorine bleaching stages, e.g. peroxide stages like ozone, hydrogenperoxide and peracetic acid, and combinations of chlorine andnon-chlorine bleaching and oxidizing stages, optionally in combinationwith reducing stages like treatment with dithionite. The clay can beadded to the cellulosic suspension directly to a bleaching stage,preferably to the mixer prior to the bleaching tower, at any pointbetween the bleaching and washing stages, and also to a washing stagewhere the clay may be partly or wholly removed, e.g. in the displacementsection.

According to another preferred embodiment of the invention, the clay isadded to a cellulosic suspension of a paper making process. The clay canbe added to the cellulosic suspension at any point of the paper makingprocess such as to the thick stock, thin stock, or to the white waterbefore it is recycled, e.g. prior to the thin stock feed box.Preferably, the clay is added to the thick stock. The cationic clay canalso be added to more than one point of the pulp and/or paper makingprocesses. For instance, in integrated pulp and paper mills, the claycan be added in the process for pulp production, and optionally also inthe process for paper production, and one or more drainage and retentionaids can be added in the process for paper production. Such processescan include dewatering the cellulosic suspension containing clay,diluting the suspension obtained, adding to the diluted suspension oneor more drainage and retention aids and dewatering the suspensioncontaining the drainage and retention aids.

The term “paper”, as used herein, include not only paper and theproduction thereof, but also other cellulosic fibre-containing sheet orweb-like products, such as for example board and paperboard, and theproduction thereof. The process can be used in the production of paperfrom different types of aqueous suspensions of cellulosic(cellulose-containing) fibres and the suspensions should suitablycontain at least 25% by weight and preferably at least 50% by weight ofsuch fibres, based on a dry substance. The cellulosic fibres can bebased on virgin and/or recycled fibres, and the suspension can be basedon fibres from chemical pulp such as sulphate, sulphite and organosolvepulps, mechanical pulp such as thermo-mechanical pulp,chemo-thermo-mechanical pulp, refiner pulp and ground wood pulp, fromboth hardwood and softwood, and can also be based on recycled fibres,optionally from de-inked pulps, and mixtures thereof. If recycled fibresare used the suspended, recycled fibres are commonly treated in order toseparate the non-fibre components such as, for example, printing inksand various paper surface treatment compounds, e.g. latex from thefibres. In a preferred embodiment, the clay is suitably added to such ade-inking treatment process.

According to the invention, the clay is suitably added to the cellulosicsuspension in an amount of from about 0.01% by weight to about 5% byweight, preferably form about 0.05% by weight up to about 2% by weight,calculated as dry clay on a dry cellulosic suspension.

The present invention also relates to a process for the production of acellulosic product, e.g. pulp and paper, which comprises adding to thesuspension a clay having 3R₂ stacking and optionally one or moredrainage (dewatering) and retention aids. In a preferred embodiment, thedrainage and retention aids comprise at least one cationic polymer. Itis preferred that the clay and drainage and retention aids are used in aprocess for the production of paper. The term “drainage and retentionaid”, as used herein, refers to a component (agent, additive) which,when being added to an aqueous cellulosic suspension, give betterdrainage and/or retention than is obtained when not adding saidcomponent. The term “cationic polymer”, as used herein, refers to anorganic polymer having one or more cationic groups, preferably anoverall cationic charge. The cationic polymer may also contain anionicgroups, and such polymers are commonly also referred to as amphotericpolymers.

The cationic polymer according to the invention can be derived fromnatural and synthetic sources. Examples of suitable cationic polymersderived from natural sources include polysaccharides, e.g. starches,guar gums, celluloses, chitins, chitosans, glycans, galactans, glucans,xanthan gums, pectins, mannans, dextrins, preferably starches and guargums. Examples of suitable starches include potato, corn, wheat,tapioca, rice, waxy maize, barley, etc. Examples of suitable synthetic,cationic polymers include chain-growth polymers, e.g. vinyl additionpolymers like acrylate-, acrylamide- and vinylamide-based polymers, andstep-growth polymers, e.g. polyurethanes. Suitably, the cationic polymeris selected from polysaccharides, e.g. starches, and vinyl additionpolymers, e.g. acryl-amide-based polymers, and mixtures thereof.

The cationic polymer, specifically cationic polysaccharides and vinyladdition polymers, may also comprise aromatic groups which can bepresent in the polymer backbone or, preferably, the aromatic groups canbe a pendent group attached to or extending from the polymer backbone orbe present in a pendent group that is attached to or extending from thepolymer backbone (main-chain). Examples of suitable aromatic groupsinclude aryl, aralkyl and alkaryl groups, e.g. phenyl, phenylene,naphthyl, phenylene, xylylene, benzyl and phenylethyl;nitrogen-containing aromatic (aryl) groups, e.g. pyridinium andquinolinium, as well as derivatives of these groups, preferably benzyl.Examples of cationically charged groups that can be present in thecationic polymer as well as in monomers used for preparing the cationicpolymer include quaternary ammonium groups, tertiary amino groups andacid addition salts thereof.

The cationic organic polymer having an aromatic group is preferably apolysaccharide represented by the general structural formula (I):

wherein P is a residue of a polysaccharide; A₁ is a group attaching N tothe polysaccharide residue, suitably a chain of atoms comprising C and Hatoms, and optionally 0 and/or N atoms, usually an alkylene group withfrom 2 to 18 and suitably 2 to 8 carbon atoms, optionally interrupted orsubstituted by one or more heteroatoms, e.g. O or N, e.g. an alkyleneoxygroup or hydroxy propylene group (—CH₂—CH(OH)—CH₂—); K₁ and K₂ are eachH or, preferably, a hydrocarbon group, suitably alkyl, having from 1 to3 carbon atoms, preferably 1 to 2 carbon atoms; Q is a substituentcontaining an aromatic group, suitably a phenyl or substituted phenylgroup, which can be attached to the nitrogen by means of an alkylenegroup usually having from 1 to 3 carbon atoms, suitably 1 to 2 carbonatoms, and preferably Q is a benzyl group (—CH₂—C₆H₅); n is an integer,usually from about 2 to about 300,000, suitably from 5 to 200,000 andpreferably from 6 to 125,000 or, alternatively, K₁, K₂ and Q togetherwith N form a aromatic group containing from 5 to 12 carbon atoms; andX⁻ is an anionic counterion, usually a halide like chloride. Suitablepolysaccharides of the general formula (I) include those mentionedabove. Cationic polysaccharides according to the invention can alsocontain anionic groups, preferably in a minor amount. Such anionicgroups may be introduced in the polysaccharide by means of chemicaltreatment or be present in the native polysaccharide.

The cationic organic polymer having an aromatic group may also be achain-growth polymer. The term “chain-growth polymer”, as used herein,refers to a polymer obtained by chain-growth polymerisation, also beingreferred to as chain reaction polymer and chain reaction polymerisation,respectively. Examples of suitable chain-growth polymers include vinyladdition polymers prepared by polymerisation of one or more monomershaving a vinyl group or ethylenically unsaturated bond, for example apolymer obtained by polymerising a cationic monomer or a monomer mixturecomprising a cationic monomer represented by the general structuralformula (II):

wherein L₃ is H or CH₃; L₁ and L₂ are each H or, preferably, ahydrocarbon group, suitably alkyl, having from 1 to 3 carbon atoms,preferably 1 to 2 carbon atoms; A₂ is O or NH; B₂ is an alkyl oralkylene group having from 2 to 8 carbon atoms, suitably from 2 to 4carbon atoms, or a hydroxy propylene group; Q is a substituentcontaining an aromatic group, suitably a phenyl or substituted phenylgroup, which can be attached to the nitrogen by means of an alkylenegroup usually having from 1 to 3 carbon atoms, suitably 1 to 2 carbonatoms, and preferably Q is a benzyl group (—CH₂—C₆H₅); and X⁻ is ananionic counterion, usually a halide like chloride.

Examples of suitable monomers represented by the general formula (II)include quaternary monomers obtained by treating dialkylaminoalkyl(meth)acrylates, e.g. dimethyl-aminoethyl (meth)acrylate,diethylaminoethyl (meth)acrylate and dimethylaminohydroxy-propyl(meth)acrylate, and dialkylaminoalkyl (meth)acrylamides, e.g.dimethylaminoethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamide,dimethylaminopropyl (meth)-acrylamide, and diethylaminopropyl(meth)acrylamide, with benzyl chloride. Preferred cationic monomers ofthe general formula (I) include dimethylaminoethylacrylate benzylchloride quaternary salt and dimethylaminoethylmethacrylate benzylchloride quaternary salt. The monomer of formula (II) can becopolymerized with one or more non-ionic, cationic and/or anionicmonomers. Suitable copolymerizable non-ionic monomers include(meth)-acrylamide; acrylamide-based monomers like N-alkyl(meth)acrylamides, N,N-dialkyl (meth)acrylamides and dialkylaminoalkyl(meth)acrylamides, acrylate-based monomers like dialkylaminoalkyl(meth)acrylates, and vinylamides. Suitable copolymerizable cationicmonomers include acid addition salts and quaternary salts ofdimethylaminoethyl (meth)acrylate and diallyldimethylammonium chloride.The cationic organic polymer may also contain anionic groups, preferablyin a minor amount. Suitable copolymerizable anionic monomers includeacrylic acid, methacrylic acid and various sulphonated vinylic monomerssuch as styrenesulphonate. Preferred copolymerizable monomers includeacrylamide and methacrylamide, i.e. (meth)acrylamide, and the cationicor amphoteric organic polymer is preferably an acrylamide-based polymer.

Cationic aromatic vinyl addition polymers according to this inventioncan be prepared from a monomer mixture generally comprising from 1 to 99mole %, suitably from 2 to 50 mole % and preferably from 5 to 20 mole %of cationic monomer having an aromatic group and from 99 to 1 mole %,suitably from 98 to 50 mole %, and preferably from 95 to 80 mole % ofother copolymerizable monomers which preferably comprises acrylamide ormethacrylamide ((meth)acrylamide), the monomer mixture suitablycomprising from 98 to 50 mole % and preferably from 95 to 80 mole % of(meth)acrylamide, the sum of percentages being 100.

Examples of suitable aromatic cationic step-growth polymers according tothe invention include cationic polyurethanes, which can be prepared froma monomer mixture comprising aromatic isocyanates and/or aromaticalcohols. Examples of suitable aromatic isocyanates includediisocyanates, e.g. toluene-2,4- and 2,6-diisocyanates anddiphenyl-methane-4,4′-diisocyanate. Examples of suitable aromaticalcohols include dihydric alcohols, i.e. diols, e.g. bisphenol A, phenyldiethanol amine, glycerol monoterephthalate and tri-methylolpropanemonoterephthalate. Monohydric aromatic alcohols such as phenol andderivatives thereof may also be employed. The monomer mixture can alsocontain non-aromatic isocyanates and/or alcohols, usually diisocyanatesand diols, for example any of those known to be useful in thepreparation of polyurethanes. Examples of suitable monomers containingcationic groups include cationic diols such as acid addition salts andquaternisation products of N-alkandiol dialkylamines and N-alkyldialkanolamines like 1,2-propanediol-3-dimethylamine, N-methyldiethanolamine, N-ethyl diethanolamine, N-propyl diethanolamine,N-n-butyl diethanolamine and N-t-butyl diethanolamine, N-stearyldiethanol-amine and N-methyl dipropanolamine. The quaternizationproducts can be derived from alkylating agents like methyl chloride,dimethyl sulphate, benzyl chloride and epichlorohydrin.

Examples of suitable cationic organic polymers having an aromatic groupthat can be used according to the present invention include thosedescribed in International Patent Application Publication Nos. WO99/55964, WO 99/55965, WO 99/67310 and WO 02/12626, which are herebyincorporated herein by reference.

The weight average molecular weight of the cationic polymer can varywithin wide limits dependent on, inter alia, the type of polymer used,and usually it is at least about 5,000 and often at least 10,000. Moreoften, it is above 150,000, normally above 500,000, suitably above about700,000, preferably above about 1,000,000 and most preferably aboveabout 2,000,000. The upper limit is not critical; it can be about200,000,000, usually 150,000,000 and suitably 100,000,000.

The cationic organic polymer, such as polysaccharides and vinyl additionpolymers, can have a degree of cationic substitution (DS_(C)) varyingover a wide range dependent on, inter alia, the type of polymer used;DS_(C) can be from 0.005 to 1.0, usually from 0.01 to 0.5, suitably from0.02 to 0.3, preferably from 0.025 to 0.2; and the degree of aromaticsubstitution (DS_(Q)) can be from 0.001 to 0.5, usually from 0.01 to0.5, suitably from 0.02 to 0.3 and preferably from 0.025 to 0.2. In casethe cationic organic polymer contains anionic groups, the degree ofanionic substitution (DS_(A)) can be from 0 to 0.2, suitably from 0 to0.1 and preferably from 0 to 0.05, the cationic polymer having anoverall cationic charge. Usually the charge density of the cationicpolymer is within the range of from 0.1 to 6.0 meqv/g of dry polymer,suitably from 0.2 to 5.0 and preferably from 0.5 to 4.0.

According to a preferred embodiment of the invention, the drainage andretention aid comprises, in addition to the cationic polymer, also ananionic material. Examples of suitable anionic materials include anionicmicroparticulate materials, e.g. anionic inorganic and organicparticles, and anionic organic polymers, e.g. anionic vinyl additionpolymers such as anionic acrylamide-based polymers.

Anionic inorganic microparticulate materials that can be used includeanionic silica-based particles and anionic clays of the smectite type.It is preferred that the anionic inorganic particles are in thecolloidal range of particle size. Anionic silica-based particles, i.e.particles based on SiO₂ or silicic acid, are preferably used and suchparticles are usually supplied in the form of aqueous colloidaldispersions, so-called sols. Examples of suitable silica-based particlesinclude colloidal silica and different types of polysilicic acid, eitherhomo- or co-polymerised. The silica-based sols can be modified andcontain other elements, e.g. aluminium, boron, nitrogen, zirconium,gallium, titanium and the like, which can be present in the aqueousphase and/or in the silica-based particles. Suitable silica-basedparticles of this type include colloidal aluminium-modified silica andaluminium silicates. Mixtures of such suitable silica-based particlescan also be used. Drainage and retention aids comprising suitableanionic silica-based particles include those disclosed in U.S. Pat. Nos.4,388,150; 4,927,498; 4,954,220; 4,961,825; 4,980,025; 5,127,994;5,176,891; 5,368,833; 5,447,604; 5,470,435; 5,543,014; 5,571,494;5,573,674; 5,584,966; 5,603,805; 5,688,482; and 5,707,493; which arehereby incorporated herein by reference.

Anionic silica-based particles suitably have an average particle sizebelow about 100 nm, preferably below about 20 nm and more preferably inthe range of from about 1 to about 10 nm. As conventional in the silicachemistry, the particle size refers to the average size of the primaryparticles, which may be aggregated or non-aggregated. The specificsurface area of the silica-based particles is suitably above 50 m²/g andpreferably above 100 m²/g. Generally, the specific surface area can beup to about 1700 m²/g and preferably up to 1000 m²/g. The specificsurface area is measured by means of titration with NaOH in a well knownmanner, e.g. as described by G. W. Sears in Analytical Chemistry 28(1956): 12, 1981-1983 and in the U.S. Pat. No. 5,176,891. The given areathus represents the average specific surface area of the particles.

According to a preferred embodiment of the invention, the anionicsilica-based particles have specific surface area within the range offrom 50 to 1000 m²/g, preferably from 100 to 950 m²/g. Sols ofsilica-based particles of these types also encompass modifications, forexample with any of the elements mentioned above. Preferably, thesilica-based particles are present in a sol having an S-value in therange of from 8 to 50%, preferably from 10 to 40%, containingsilica-based particles with a specific surface area in the range of from300 to 1000 m²/g, suitably from 500 to 950 m²/g, and preferably from 750to 950 m²/g, which sols can be modified as mentioned above. The S-valuecan be measured and calculated as described by Iler & Dalton in J. Phys.Chem. 60 (1956), 955-957. The S-value indicates the degree ofaggregation or microgel formation and a lower S-value is indicative of ahigher degree of aggregation.

According to another preferred embodiment of the invention, thesilica-based particles are selected from polysilicic acid, either homo-or co-polymerised, having a high specific surface area, suitably aboveabout 1000 m² μg. The specific surface area can be within the range offrom 1000 to 1700 m²/g and preferably from 1050 to 1600 m²/g. The solsof modified or co-polymerised polysilicic acid can contain otherelements as mentioned above. In the art, polysilicic acid is alsoreferred to as polymeric silicic acid, polysilicic acid microgel,polysilicate and polysilicate microgel, which all are encompassed by theterm poly-silicic acid used herein. Aluminium-containing compounds ofthis type are commonly also referred to as polyaluminosilicate andpolyaluminosilicate microgel, which are both, encom-passed by the termscolloidal aluminium-modified silica and aluminium silicate used herein.

According to yet another preferred embodiment of the invention, thedrainage and retention aid comprise anionic clay of the smectite type.Examples of suitable smectite clays include natural clays such asmontmorillonite/bentonite, hectorite, beidelite, nontronite andsaponite, as well as synthetic smectite-like clays such as laponite,etc., preferably bentonite and especially such bentonite which afterswelling preferably has a surface area of from 200 to 800 m²/g. Suitableanionic clays include those disclosed in U.S. Pat. Nos. 4,753,710;5,071,512; and 5,607,552, which are hereby incorporated herein byreference. Also mixtures of anionic silica-based particles and anionicclays of the smectite type can be employed.

Anionic organic polymers according to the invention contain one or morenegatively charged (anionic) groups. Examples of groups that can bepresent in the polymer as well as in the monomers used for preparing thepolymer include groups carrying an anionic charge and acid groupscarrying an anionic charge when dissolved or dispersed in water, thegroups herein collectively being referred to as anionic groups, such asphosphate, phosphonate, sulphate, sulphonic acid, sulphonate, carboxylicacid, carboxylate, alkoxide and phenolic groups, i.e.hydroxy-substituted phenyls and naphthyls. Groups carrying an anioniccharge are usually salts of an alkali metal, alkaline earth or ammonia.

Anionic organic particles that can be used according to the inventioninclude cross-linked anionic vinyl addition polymers, suitablycopolymers comprising an anionic monomer like acrylic acid, methacrylicacid and sulfonated or phosphonated vinyl addition monomers, usuallycopolymerised with non-ionic monomers like (meth)acrylamide, alkyl(meth)-acrylates, etc. Useful anionic organic particles also includeanionic condensation polymers, e.g. melamine-sulfonic acid sols.

Further anionic polymers that can form part of the drainage andretention system include vinyl addition polymers comprising an anionicmonomer having carboxylate groups like acrylic acid, methacrylic acidethylacrylic acid, crotonic acid, itaconic acid, maleic acid and saltsof any of the foregoing, anhydrides of the diacids, and sulfonated vinyladdition monomers, such as sulfonated styrene, usually copolymerisedwith non-ionic monomers like acrylamide, alkyl acrylates, etc., forexample those disclosed in U.S. Pat. Nos. 5,098,520 and 5,185,062, theteachings of which are hereby incorporated herein by reference Theanionic vinyl addition polymers suitably have weight average molecularweights from about 50,000 to about 5,000,000, typically from about75,000 to about 1,250,000.

Examples of suitable anionic organic polymer further include step-growthpolymers, chain-growth polymers, polysaccharides, naturally occurringaromatic polymers and modifications thereof. The term “step-growthpolymer”, as used herein, refers to a polymer obtained by step-growthpolymerisation, also being referred to as step-reaction polymer andstep-reaction polymerisation, respectively. The anionic organic polymerscan be linear, branched or cross-linked. Preferably the anionic polymeris water-soluble or water-dispersable. In a preferred embodiment, theanionic organic polymer also contains one or more aromatic groups.

Anionic organic polymers having aromatic groups contain one or morearomatic groups of the same or different types. The aromatic group ofthe anionic polymer can be present in the polymer backbone or in asubstituent group that is attached to the polymer backbone (main chain).Examples of suitable aromatic groups include aryl, aralkyl and alkarylgroups and derivatives thereof, e.g. phenyl, tolyl, naphthyl, phenylene,xylylene, benzyl, phenylethyl and derivatives of these groups.

Examples of suitable anionic aromatic step-growth polymers includecondensation polymers, i.e. polymers obtained by step-growthcondensation polymerisation, e.g. condensates of an aldehyde such asformaldehyde with one or more aromatic compounds containing one or moreanionic groups, and optional other co-monomers useful in thecondensation polymerisation such as urea and melamine. Examples ofsuitable aromatic compounds containing anionic groups comprises benzeneand naphthalene-based compounds containing anionic groups such asphenolic and naphtholic compounds, e.g. phenol, naphthol, resorcinol andderivatives thereof, aromatic acids and salts thereof, e.g. phenylic,phenolic, naphthylic and naphtholic acids and salts, usually sulphonicacids and sulphonates, e.g. benzene sulphonic acid and sulphonate, xylensulphonic acid and sulphonates, naphthalene sulphonic acid andsulphonate, phenol sulphonic acid and sulphonate. Examples of suitableanionic step-growth polymers according to the invention include anionicbenzene-based and naphthalene-based condensation polymers, preferablynaphthalene-sulphonic acid based and naphthalene-sulphonate basedcondensation polymers.

Examples of further suitable anionic step-growth polymers havingaromatic groups include addition polymers, i.e. polymers obtained bystep-growth addition polymerisation, e.g. anionic polyurethanes, whichcan be prepared from a monomer mixture comprising aromatic isocyanatesand/or aromatic alcohols. Examples of suitable aromatic isocyanatesinclude diisocyanates, e.g. toluene-2,4- and 2,6-diisocyanates anddiphenylmethane-4,4′-diisocyanate. Examples of suitable aromaticalcohols include dihydric alcohols, i.e. diols, e.g. bisphenol A, phenyldiethanol amine, glycerol monoterephthalate and trimethylolpropanemonoterephthalate. Monohydric aromatic alcohols such as phenol andderivatives thereof may also be employed. The monomer mixture can alsocontain non-aromatic isocyanates and/or alcohols, usually diisocyanatesand diols, for example any of those known to be useful in thepreparation of polyurethanes. Examples of suitable monomers containinganionic groups include the monoester reaction products of triols, e.g.trimethylolethane, tri-methylolpropane and glycerol, with dicarboxylicacids or anhydrides thereof, e.g. succinic acid and anhydride,terephthalic acid and anhydride, such as glycerol monosuccinate,glycerol monoterephthalate, trimethylolpropane monosuccinate,trimethylolpropane monoterephthalate, N,N-bis-(hydroxyethyl)-glycine,di-(hydroxymethyl)propionic acid,N,N-bis-(hydroxyethyl)-2-aminoethanesulphonic acid, and the like,optionally and usually in combination with reaction with a base, such asalkali metal and alkaline earth hydroxides, e.g. sodium hydroxide,ammonia or an amine, e.g. triethylamine, thereby forming an alkalimetal, alkaline earth or ammonium counter-ion.

Examples of suitable anionic chain-growth polymers having aromaticgroups include anionic vinyl addition polymers obtained from a mixtureof vinylic or ethylenically unsaturated monomers comprising at least onemonomer having an aromatic group and at least one monomer having ananionic group, usually co-polymerised with non-ionic monomers such asacrylate- and acrylamide-based monomers. Examples of suitable anionicmonomers include (meth)acrylic acid and paravinyl phenol (hydroxystyrene).

Examples of suitable anionic polysaccharides having aromatic groupsinclude starches, guar gums, celluloses, chitins, chitosans, glycans,galactans, glucans, xanthan gums, pectins, mannans, dextrins, preferablystarches, guar gums and cellulose derivatives, suitable starchesincluding potato, corn, wheat, tapioca, rice, waxy maize and barley,preferably potato. The anionic groups in the polysaccharide can benative and/or introduced by chemical treatment. The aromatic groups inthe polysaccharide can be introduced by chemical methods known in theart.

Naturally occurring aromatic anionic polymers and modifications thereof,i.e. modified naturally occurring aromatic anionic polymers, accordingto the invention include naturally occurring polyphenolic substancesthat are present in wood and organic extracts of bark of some woodspecies and chemical modifications thereof, usually sulphonatedmodifications thereof. The modified polymers can be obtained by chemicalprocesses such as, for example, sulphite pulping and kraft pulping.Examples of suitable anionic polymers of this type include lignin-basedpolymers, preferably sulphonated lignins, e.g. ligno-sulphonates, kraftlignin, sulphonated kraft lignin, and tannin extracts.

The weight average molecular weight of the anionic polymer havingaromatic groups can vary within wide limits dependent on, inter alia,the type of polymer used, and usually it is at least about 500, suitablyabove about 2,000 and preferably above about 5,000. The upper limit isnot critical; it can be about 200,000,000, usually about 150,000,000,suitably about 100,000,000 and preferably about 10,000,000.

The anionic polymer having aromatic groups can have a degree of anionicsubstitution (DS_(A)) varying over a wide range dependent on, interalia, the type of polymer used; DS_(A) is usually from 0.01 to 2.0,suitably from 0.02 to 1.8 and preferably from 0.025 to 1.5; and thedegree of aromatic substitution (DS_(Q)) can be from 0.001 to 1.0,usually from 0.01 to 0.8, suitably from 0.02 to 0.7 and preferably from0.025 to 0.5. In case the anionic polymer contains cationic groups, thedegree of cationic substitution (DS_(C)) can be, for example, from 0 to0.2, suitably from 0 to 0.1 and preferably from 0 to 0.05, the anionicpolymer having an overall anionic charge. Usually the anionic chargedensity of the anionic polymer is within the range of from 0.1 to 6.0meqv/g of dry polymer, suitably from 0.5 to 5.0 and preferably from 1.0to 4.0.

Examples of suitable aromatic, anionic organic polymers that can be usedaccording to the present invention include those described in U.S. Pat.Nos. 4,070,236 and 5,755,930; and International Patent ApplicationPublication Nos. WO 95/21295, WO 95/21296, WO 99/67310, WO 00/49227 andWO 02/12626, which are hereby incorporated herein by reference.

Further to the above mentioned cationic and anionic drainage andretention aids, low molecular weight cationic organic polymers and/orinorganic aluminium compounds can also be used as drainage and retentionaids.

Low molecular weight (hereinafter called LMW) cationic organic polymersthat can be used in conjunction with the dewatering and retention aidinclude those commonly referred to and used as anionic trash catchers(ATC). ATC's are known in the art as neutralising and/or fixing agentsfor disturbing/detrimental anionic substances present in the stock andthe use thereof in combination with drainage and retention aids oftenprovide further improved drainage and/or retention. The LMW cationicorganic polymer can be derived from natural or synthetic sources, andpreferably it is a LMW synthetic polymer. Suitable organic polymers ofthis type include LMW highly charged cationic organic polymers such aspolyamines, polyamidoamines, polyethyleneimines, homo- and copolymersbased on diallyidimethyl ammonium chloride, (meth)acrylamides and(meth)acrylates, vinylamide-based and polysaccarides. In relation to themolecular weight of the retention and dewatering polymers, the weightaverage molecular weight of the LMW cationic organic polymer ispreferably lower; it is suitably at least about 2,000 and preferably atleast about 10,000. The upper limit of the molecular weight is usuallyabout 2,000,000, to about 3,000,000. Suitable LMW polymers may have aweight average molecular weight of from about 2,000 up to about2,000,000.

Aluminium compounds that can be used as ATC's, according to theinvention include alum, aluminates, aluminium chloride, aluminiumnitrate and polyaluminium compounds, such as polyaluminium chlorides,polyaluminium sulphates, polyaluminium compounds containing bothchloride and sulphate ions, polyaluminium silicate-sulphates, andmixtures thereof. The polyaluminium compounds may also contain otheranions than chloride ions, for example anions from sulfuric acid,phosphoric acid, and organic acids such as citric acid and oxalic acid.

According to one preferred embodiment of the invention, the drainage andretention aid comprises a cationic polymer and an anionic inorganicmicroparticulate material, suitably anionic silica-based particles oranionic clay of the smectite type. According to another preferredembodiment of the invention, the drainage and retention aid comprises acationic polymer and an anionic vinyl addition polymer, suitably ananionic acrylamide-based polymer. According to yet another preferredembodiment of the invention, the drainage and retention aid comprises acationic polymer comprising aromatic groups. According to yet anotherpreferred embodiment of the invention, the drainage and retention aidcomprises a cationic polymer comprising aromatic groups and an anionicpolymer comprising aromatic groups.

The components of drainage and retention aids can be added to thecellulosic suspension in conventional manner and in any order. Whenusing an anionic micro-particulate material, it is preferred to add thecationic polymer to the suspension before adding the microparticulatematerial, even if the opposite order of addition may be used. It isfurther preferred to add the cationic polymer before a shear stage,which can be selected from pumping, mixing, cleaning, etc., and to addthe anionic compound after that shear stage. When using an LMW cationicorganic polymer and/or an aluminium compound, such components arepreferably introduced into the suspension prior to introducing thecationic polymer and anionic component, if used. Alternatively, the LMWcationic organic polymer and cationic polymer can be introduced into thesuspension essentially simultaneously, either separately or inadmixture, e.g. as disclosed in U.S. Pat. No. 5,858,174, which is herebyincorporated herein by reference.

If the clay according to the invention is used together with a drainageand retention aid, the clay can be added to the suspension prior to orafter the addition of the drainage and retention aid. However, it ispreferred that the cationic clay is added prior to the addition ofdrainage and retention aid and other performance chemicals. Suitably,the clay is added to the thick stock, or to the thin stock, and thedrainage and retention aid is added to the thin stock. The clay can alsobe added to the re-cycled white water. If two or more drainage andretention aids are used, i.e. a cationic polymer together with ananionic material, e.g. silica-based particles, or anionic organicpolymer, the clay may be added to the cellulosic suspension (stock)prior to, after or in between the addition of the drainage and retentionaids, or together with any of the drainage and retention aids. The claymay also be added at several locations in the process, e.g. to the thickstock and again to the thin stock prior to the addition of drainage andretention aid.

The drainage and retention aid(s) according to the invention can beadded to the stock to be dewatered in amounts which can vary within widelimits depending on, inter alia, type and number of components, type ofcellulosic suspension, salt content, type of salts, filler content, typeof filler, point of addition, degree of white water closure, etc.Generally, the retention and drainage aid(s) are added in amounts thatgive better drainage and/or retention than is obtained when not addingthe components. The cationic polymer is usually added in an amount of atleast about 0.001% by weight, often at least about 0.005% by weight,based on dry cellulosic suspension, and the upper limit is usually about3% and suitably about 1.5% by weight. Commonly applied addition amountsof cationic polymer are from about 0.01% up to about 0.5% by weight.Anionic materials, e.g. anionic silica-based particles, anionic clays ofthe smectite type and anionic organic polymers, are usually added in anamount of at least about 0.001% by weight, often at least about 0.005%by weight, based on dry cellulosic suspension, and the upper limit isusually about 1.0% and suitably about 0.6% by weight.

When using an LMW cationic organic polymers in the process, they can beadded in an amount of at least about 0.001% by weight, based on drycellulosic suspension. Suit-ably, the amount is in the range of fromabout 0.07 up to about 0.5%, preferably in the range from about 0.1 upto about 0.35%. When using an aluminium compound in the process, thetotal amount introduced into the stock to be dewatered depends on thetype of aluminium compound used and on other effects desired from it. Itis for instance well known in the art to utilize aluminium compounds asprecipitants for rosin-based sizing agents. The total amount added isusually at least about 0.05% by weight, calculated as Al₂O₃ and based ondry cellulosic suspension. Suitably the amount is in the range of fromabout 0.5 u to about 3.0%, preferably in the range from about 0.1 up toabout 2.0%.

Further additives which are conventional in papermaking can of course beused in combination with the additive(s) according to the invention,such as, for example, dry strength agents, wet strength agents, opticalbrightening agents, dyes, sizing agents like rosin-based sizing agentsand cellulose-reactive sizing agents, e.g. ketene dimers and succinicanhydrides, etc. The cellulosic suspension, or stock, can also containmineral fillers of conventional types such as, for example, kaolin,china clay, titanium dioxide, gypsum, talc and natural and syntheticcalcium carbonates such as chalk, ground marble and precipitated calciumcarbonate.

Furthermore, the process can also be useful in the manufacture of paperfrom cellulosic suspensions having high conductivity. In such cases, theconductivity of the suspension that is dewatered on the wire is usuallyat least 1.0 mS/cm, suitably at least 2.0 mS/cm, and preferably at least3.5 mS/cm. Conductivity can be measured by standard equipment such as,for example, a WTW LF 539 instrument supplied by Christian Bemer. Thevalues referred to above are suitably determined by measuring theconductivity of the cellulosic suspension that is fed into or present inthe head box of the paper machine or, alternatively, by measuring theconductivity of white water obtained by dewatering the suspension. Highconductivity levels mean high contents of salts (electrolytes) which canbe derived from the materials used to form the cellulosic suspension,from various additives introduced into the cellulosic suspension, fromthe fresh water supplied to the process, etc. Further, the content ofsalts is usually higher in processes where white water is extensivelyrecirculated, which may lead to considerable accumulation of salts inthe water circulating in the process.

The present invention further encompasses paper making processes wherewhite water is extensively recycled, or recirculated, i.e. with a highdegree of white water closure, for example where from 0 to 30 tons offresh water are used per ton of dry paper produced, usually less than20, suitably less than 15, preferably less than 10 and notably less than5 tons of fresh water per ton of paper. Recycling of white waterobtained in the process suitably comprises mixing the white water withcellulosic fibres and/or optional fillers to form a suspension to bedewatered; preferably it comprises mixing the white water with asuspension containing cellulosic fibres, and optional fillers, beforethe suspension enters the forming wire for dewatering. The white watercan be mixed with the suspension before, between, simultaneous with orafter introducing the clay and optional drainage and retention aid(s) ofthis invention. Fresh water can be introduced in the process at anystage; for example, it can be mixed with cellulosic fibres in order toform a suspension, and it can be mixed with a thick suspensioncontaining cellulosic fibres to dilute it so as to form a thinsuspension to be dewatered, before, simultaneous with or after mixingthe suspension with white water.

The invention is further illustrated in the following Examples which,however, are not intended to limit the same. Parts and % relate to partsby weight and % by weight, respectively, unless otherwise stated.

EXAMPLE 1

An Al—Mg clay having the 3R₂ stacking (CC-14, Akzo Nobel Catalyst B.V.)was compared to a commercial talc (Finntalc PO₅ from Omya) in terms ofpitch adsorption. The method of evaluation of pitch adsorption ofmineral powder was a variation of a procedure outlined by D. A. Hughesin Tappi (July 1977, vol. 60, No. 7, p. 144-146). Firstly, samples ofsynthetic pitch were prepared by adding potassium hydroxide (1 M) to amixture of 0.65 g of gum rosin and 0.35 g of oleic acid untilsaponification resulted. Denatured ethanol was subsequently added todissolve the synthetic pitch.

Pitch adsorption test procedure: 35 ml of distilled water was firstadded to a glass centrifuge tube followed by the addition of 1 ml of thesynthetic pitch solution and 10 ml of clay having the 3R₂ stacking (2.5%dry content). The pH of the synthetic pitch slurry was adjusted to 6.5with sulphuric acid. The mixture was subsequently stirred for 2 minutesand centrifuged for 20 minutes at 4500 rpm. The supernatant wasthereafter poured off and discarded and the tube was dried over night at60° C. After drying, the 10 ml of a chloroform-acetic anhydride (1:1)reagent was added to the tube and stirred to release the adsorbed pitch.The tube was then centrifuged for 20 minutes effecting that the clearreagent remained at the top of the tube. The reagent was thereafterpoured into a small beaker and 10 drops of conc. sulphuric acid wereadded. After a period of 4 minutes the liquid was measured on an UV-visspectrophotometer set at 400 nm whereby the absorbance value wascompared to absorbance values of known quantities of pitch. Similar testwas also performed for the sample of Finntalc P05. The pitch adsorptionresults are summarised in Table 1, in which ‘Pitch Addition’ refers tothe amount of pitch, in mg, added per gram of adsorbent; talc or clay,and ‘Pitch Adsorption’ refers to the amount of pitch, in mg, adsorbedper gram of adsorbent; talc or clay. TABLE 1 Pitch Adsorption [mg/g]Clay Clay Pitch Talc (CC-14) Talc (CC-14) Test Addition [0.16 [0.16[0.08 [0.08 No. [mg/g] mg/ml] mg/ml] mg/ml] mg/ml] 1 0 0 0 0 0 2 2 1.2 21.2 2 3 4 2.3 4 1.2 4 4 6 3 6 1.5 6 5 8 3.1 7.5 1.6 8 6 10 4 9 2 10 7 124.3 10 2.1 11.5 8 14 4.2 10.1 2.2 13 9 16 4.5 10.1 2 13 10 18 4.7 11 2.413

As shown by Table 1, the clay having the 3R₂ stacking has asignificantly improved adsorption capability as compared to talc.

EXAMPLE 2

In this example, the pitch adsorption characteristics of an Al—Mgcationic clay having the 3R₁, stacking, (CC-8, Süd Chemie) was comparedto an Al—Mg cationic clay having the 3R₂ stacking (CC-17, Akzo NobelCatalyst B.V.).

Two mixtures of synthetic pitch were prepared, one containing oleic acidand gum rosin (Pitch No. 1)—of example 1, and a further synthetic pitchmixture containing abietic acid. The abietic acid containing pitch(Pitch No. 2) was prepared by mixing 1 g of abietic acid and 1Mpotassium hydroxide until saponification occurred. Denaturated ethanol(250 ml) was added to dissolve the synthetic pitch. The same pitchadsorption test procedure as outlined in Example 1 was used. The resultsare summarized in Tables 1 and 2. TABLE 2 Pitch Addition (Pitch No. 1)Pitch Adsorption [mg/g] Test No. [mg/g] CC-8 (3R₁) CC-17 (3R₂) 1 0 0 0 28 5.4 7.1 3 16 9.64 14.1 4 32 21.5 29 5 48 34.4 41

TABLE 3 Pitch Addition (Pitch No. 2) Pitch Adsorption [mg/g] Test No.[mg/g] CC-8 (3R₁) CC-17 (3R₂) 1 0 0 0 2 8 4.45 6.07 3 16 11.1 13.8 4 3226.5 30.3 5 48 40.3 47.5

As shown by Tables 2 and 3, the clay with 3R₂ stacking adsorbed abieticacid and the gum rosin as well as the oleic acid mixture to asignificantly higher degree than the cationic clay having the 3R₁,stacking.

EXAMPLE 3

The adoption of stickies (hot-melts) of an Al—Mg cationic clay havingthe 3R₂ stacking (CC-14, Akzo Nobel Catalyst B.V.) was compared to talc(Finntalc P05, Omya) using the TOC Instrument (Dohrman DC190). The TOC(Total Organic Carbon) was determined by combustion at 800° C. wherebythe carbon was oxidised to carbon dioxide and then analysed by means ofthe IR-spectroscopy method. The results are summarised in Table 4, inwhich ‘Stickies Addition’ refers to the amount of stickies, in mg, addedper gram of adsorbent; clay or talc, and ‘Stickies Adsorption’ refers tothe amount of stickies, in mg, adsorbed per gram of adsorbent; talc orclay. TABLE 4 Stickies Adsorption [mg/g] Talc CC-14 Talc CC-14 Stickies[0.16 [0.16 [0.08 [0.08 Test Addition mg/ml] mg/ml] mg/ml] mg/ml] No.[mg/g] hotmelt hotmelt hotmelt hotmelt 1 0 0 0 0 0 2 2 1.3 2 1.5 2 3 41.8 4 1.8 4

EXAMPLE 4

Drainage performance by incorporation of the clay having the 3R₂stacking in a dewatering and retention aid was evaluated by means of aDynamic Drainage Analyser (DDA), available from Akribi Kemikonsulter AB,Sweden, which measures the time for draining a set volume of stockthrough a wire when removing a plug and applying vacuum (0.35 bar) tothat side of the wire which is opposite to the side on which the stockis present. First pass retention was evaluated by means of anephelometer by measuring the turbidity of the filtrate, the whitewater, obtained by draining the suspension.

The furnish used was based on a de-inking pulp from a newspaper millhaving consistency of 30 g/liter, conductivity of around 1500 μS/cm andthe pH of 7. Sample of an Al—Mg cationic clay having the 3R₂ stacking(CC-9, Akzo Nobel. Catalyst B.V.) was added to the pulp suspension. Thefurnish was then mixed with a magnetic stirrer and the dwell/contacttime of the stock and cationic clay was from 30 min. up to 1 hour.Thereafter the furnish was diluted with water (approx. 1:10) beforemaking the DDA test.

The stock/furnish samples were put into the baffled DDA-jar at time 0.Next the retention/dewatering chemicals were added in the followingorder: i) after 15 seconds 0.8 kg/ton of dry pulp of polyacrylamide (EkaPL 1510), ii) after another 15 seconds (30 seconds from the start) 0.4kg/ton of dry pulp of anionic silica-based particles (Eka NP 780), iii)after another 15 seconds draining of the suspension while automaticallyrecording the drainage time.

The filtrate samples from the drainage tests were evaluated with respectto the pitch adsorption. The adsorption was assumed to correlate toUV-vis spectrophotometer absorbance at 280 nm of the filtrate and thedecrease in UV-vis absorbance was referred to as Pitch reduction. Theresults are set forth in Table 5. TABLE 5 Addition of Test No. CC-9[kg/t] Drainage time [s] Pitch reduction [%] 1 0 9.3 — 2 5 6.04 19.8 310 5.63 21.4

Table 5 clearly shows that the addition of CC-9 to the suspensionreduces the drainage time and that the filtrate contains less pitch asthe CC-9 is added to the suspension.

EXAMPLE 5

In this example an Al—Mg cationic clay having the 3R₁ stacking (CC-12)was compared to an Al—Mg cationic clay having the 3R₂ stacking (CC-18)with respect to drainage. The same furnish and procedure as described inExample 4 was used. Table 6 summarized the results. TABLE 6 Drainagetime [sec.] Test No. CC Dosage [kg/t] CC-12 (3R₁) CC-18 (3R₂) 1 0 16.216.2 2 2 15 13.1 3 5 14.9 13.2 4 10 14.8 11.9

From table 6 it is evident that the addition of the clay having the 3R₂stacking further improves drainage compared to the cationic clay havingthe 3R₂, stacking.

EXAMPLE 6

The drainage enhancing effect of the Al—Mg cationic clay having the 3R₂stacking (CC-22) was here evaluated. The same furnish and procedure asdescribed in example 4 was used, except that different drainage andretention aids were used. In this example, 0.4 kg/ton of dry pulp ofPercol 63 (a cationic polyacrylamide from CIBA) and 2 kg/ton of dry pulpof Hydrocol SW (bentonite clay of the smectite type from CIBA) wereadded in a similar manner. TABLE 7 Drainage time [sec.] CC Dosage [kg/t]CC-22 (3R₂) 0 11.2 2 9.1 10 8.1

Table 7 demonstrates that the performance of a dewatering and retentionaid comprising addition of cationic PAM and bentonite clay to asuspension is improved by the addition of an Al—Mg cationic clay of the3R₂ type.

EXAMPLE 7

The adsorption of Pressure-Sensitive Adhesives stickies of an Al—Mgcationic clay having the 3R₂ stacking (CC-17, Akzo Nobel Catalyst B.V.)was evaluated and compared with talc (Finntalc P05, Omya).Pressure-Sensitive Adhesives stickles are found in office wastefurnishes as labels, tapes, self-sealing envelopes and Post-it® notes.

60 g of Post-it® (notes having one side totally covered with theadhesive (Tappi journal vol. 79 no 7 Jul. 1996) were cut into smallsquares and soaked in 1.5 l of cold tap water for 24 hours. 0.5 l of asalt solution containing CaCl₂.2H₂O, Na₂SO₄ 10H₂O and tap water wasadded to the water-paper mixture to simulate the paper mill conditions,such as pH and conductivity. The mixture was then disintegrated in astandard pulp disintegrator for 30000 revolutions. Fibres and fineslarger than 25 um were removed by filtration. The filtrate was heated ina water bath to 60 C. The pH varied between 6.8 and 7.4. To the filtratesamples was added Al—Mg clay having a 3R₂ stacking and Talc (P05). Afteraddition of CC-17 and talc the filtrate was mixed with a magnet stirrerand the dwell time of the CC-17 and talc was 60 min. The adsorption testwas carried out by centrifugation 30 min 4500 rpm. The supernatant wasthen poured off and TOC was measured. Table 8 shows the results ofadsorption of pressure sensitive adhesive. TABLE 8 Test No. Talc [kg/t]CC-17 [kg/t] TOC [ppm] 1 0 0 550 2 5 525 3 10 498 4 20 400 5 5 401 6 10292 7 20 115

As shown by table 8, the adsorption of pressure sensitive adhesives issignificantly improved when adding CC-17 compared to talc.

EXAMPLE 8

In this example, sizing performance was evaluated. A furnish from aliquid packaging board mill was treated with an Al—Mg cationic clayhaving the 3R₂ stacking (CC-22, Akzo Nobel Catalyst B.V.) and with talc(Finntalc P05, Omya) respectively. Size and retention chemicals wereadded and hand sheets were made (SCAN-C 26:76). Sizing of the sheets wasmeasured as Cobb 60 values (SCAN-P 12:64).

The furnish used was a thick-stock from a LPB mill, containing bleachedsoft- and hardwood pulp. This furnish was stirred and heated to 50° C.The chemicals were added and the furnish was treated for 30 minutes. Thethick stock was then diluted with tap water to a consistency of 5 g/L.This furnish had a pH of 8 and a conductivity of 0.7 mS/cm. Before sheetmaking, 0.3 kg/ton of dry pulp of AKD (Keydime C223, Eka Chemicals), 8kg/ton of dry pulp of cationic starch (Perlbond 970) and 0.5 kg/ton ofdry pulp of silica-based particles (Eka NP 590, Eka Chemicals) wereadded. The sheets had a basis weight of approximately 73 g/m². Table 9shows the sizing results obtained by addition of different amounts oftalc and CC-22 to the liquid packaging board furnish. TABLE 9 Test No.Talc [kg/t] CC-22 [kg/t] Cobb 60 1 0 0 40 2 1 44 3 5 60 4 1 35 5 5 34

The sizing performance improved when CC-22 was used over talc.

EXAMPLE 9

performance was evaluated with higher additions of Al—Mg cationic clayhaving the 3R₂ stacking (CC-22, Akzo Nobel Catalyst B.V.) and talc(Finntalc P05, Omya), respectively. Hand sheets were made, and sizingwas measured as Cobb 60 (SCAN-P 12:64) values.

The furnish used was a thick stock from a LPB mill containing hydrogenperoxide bleached soft- and hardwood sulphate pulp at ˜4% consistency.This furnish was stirred and heated to 50° C. Cationic clay or talc wereadded and the furnish was treated for 20 minutes. The thick stock wasthen diluted with bleach filtrate to ˜3.9 g/l consistency. To thefurnish AKD, 1.6 kg/t rosin size, 1.6 kg/t alum, 5.0 kg/t cationicstarch and 0.35 kg/t silica-based particles (Eka NP 590, Eka Chemicals)were added before making hand sheets (Rapid-Köthen former). The sheetshad a basis weight of approximately 100 g/m². Table 10 summarized thesizing results obtained by sizing the liquid packaging board furnish.TABLE 10 Test No. AKD [kg/t] Talc [kg/t] CC-22 [kg/t] COBB 60 1 0 0 0258 2 0.5 0 0 250 3 0.8 0 0 131 4 1 0 0 59 5 1.4 0 0 39 6 0.5 5 0 211 70.8 5 0 115 8 1 5 0 61 9 1.4 5 0 39 10 0.5 0 10 198 11 0.8 0 10 87 12 10 10 45 13 1.4 0 10 33

Table 10 shows that the sizing performance was improved (lower Cobb 60values) using CC-22 compared to talc.

EXAMPLE 10

This example was made in a pulp mill. Chemical pulp from the dewateringheadbox of the pulp machine was treated with an Al—Mg cationic clayhaving the 3R₂ stacking (CC-22, Akzo Nobel Catalyst B.V.). The turbidityof the pulp filtrate was then measured, see table 11.

The pulp used was a bleached eucalyptus fibre suspension at ˜1.2%consistency. This pulp was stirred and heated at 60° C. The cationicclay was added and the pulp was treated for 30 minutes. The pulp wasthen filtrated through a Brift-Jar with a 200 mesh wire (76.2 μm holediameters). The filtrate was analysed for turbidity in a Hach 2100Pturbidity meter. Table 11 shows the results in terms of turbidity of thefiltrate TABLE 11 Test No. CC-22 [kg/t] Turbidity [NTU] 1 0 53 2 2 43 35 23

The turbidity of the filtrate improved (decreased) when treating achemical pulp with CC-22.

EXAMPLE 11

This example was made in a TMP pulp mill. Thermomechanical pulp (TMP)was dewatered or washed after hydrogen peroxide bleaching. The filtrateis often referred to as bleach filtrate. TMP bleach filtrate water wasstirred and heated at 50° C. The TMP bleach filtrate water was treatedfor 30 minutes with an Al—Mg cationic clay having the 3R₂ stacking(CC-22, Akzo Nobel Catalyst B.V.). This water was centrifuged and theclear phase was measured for turbidity by being analysed for absorptionin a Lasa 10 spectrophotometer at 700 nm wavelength. Table 12 shows theresults. TABLE 12 Test No. CC-22 [kg/t] Absorption [700 nm] 1 0 0.506 210 0.377

The absorption in the clear phase improved (decreased) when treating TMPbleach water with CC-22.

EXAMPLE 12

This example was made in a de-inked pulp (DIP) mill. Pulp from the DIPplant was treated with an Al—Mg cationic clay having the 3R₂ stacking(CC-22, Akzo Nobel Catalyst B.V.). The turbidity of the pulp filtratewas then measured, see table 13.

The pulp used was a taken from between the disc filter and the screwpress in the DIP plant. The pulp had a consistency of ˜7%, and wasdiluted with tap water to ˜4.2%. This pulp was stirred and heated at 50°C. The clay was added and the pulp was treated for 30 minutes. The pulpwas then filtrated through a GF/A glass fibre filter (˜2 μm holediameters). The filtrate was analysed for turbidity in a Hach 2100Pturbidity meter. Table 13 shows the results. TABLE 13 Test No. CC-22[kg/t] Turbidity [NTU] 1 0 71.8 2 2 63.5 3 5 42.3

The turbidity of the filtrate improved (decreased) when mixing de-inkedpulp with CC-22 before filtering.

EXAMPLE 13

Pulp from a de-inked pulp (DIP) mill was treated with an Al—Mg cationicclay having the 3R₂ stacking (CC-22, Akzo Nobel Catalyst B.V.) in amanner similar to Example 12. The turbidity of the pulp filtrate wasthen measured and is summarized in Table 14. TABLE 14 test CC-22 [kg/t]Turbidity [NTU] 1 0 18 2 5 15 3 10 11

The turbidity of the filtrate improves (decreases) when treating ade-inked pulp by adding CC-22 to it before filtering.

1.-8. (canceled)
 9. A process for the production of paper whichcomprises (i) providing an aqueous cellulosic suspension; (ii) adding tothe suspension a clay having 3R₂ stacking, the clay being added in anamount of at least about 0.01% by weight, calculated as dry clay on drycellulosic suspension; and (iii) dewatering the obtained suspension. 10.The process according to claim 9, wherein the clay is cationic.
 11. Theprocess according to claim 9, wherein the clay is hydrotalcite.
 12. Theprocess according to claim 9, wherein it further comprises adding to thesuspension one or more drainage and retention aids.
 13. The processaccording to claim 12, wherein the drainage and retention aids comprisecationic polymer and anionic material.
 14. The process according toclaim 13, wherein the drainage and retention aids comprise cationicpolymer and anionic silica-based particles.
 15. The process according toclaim 13, wherein the drainage and retention aids comprise cationicpolymer and anionic clay of smectite type.
 16. The process according toclaim 12, wherein the drainage and retention aids comprise cationic andanionic organic polymers.
 17. The process according to claim 13, whereinthe cationic polymer is cationic starch or cationic acrylamide-basedpolymer.
 18. The process according to claim 16, wherein the cationicpolymer is cationic starch or cationic acrylamide-based polymer.
 19. Theprocess according to claim 13, wherein the cationic polymer contains oneor more aromatic groups.
 20. The process according to claim 9, whereinit further comprises adding to the suspension one or more sizing agents.21. A process for the production of paper which comprises (i) providingan aqueous cellulosic suspension; (ii) adding to the suspension acationic clay in an amount of at least about 0.01% by weight, calculatedas dry clay on dry cellulosic suspension; (iii) adding to the suspensionone or more drainage and retention aids comprising at least one cationicpolymer, the cationic polymer being added in an amount of at least about0.001% by weight, based on dry cellulosic suspension, (iv) dewateringthe obtained suspension.
 22. The process according to claim 21, whereinthe clay has 3R₂ stacking.
 23. The process according to claim 21,wherein the drainage and retention aids comprise cationic polymer andanionic silica-based particles.
 24. The process according to claim 23,wherein the silica-based particles have a specific surface area above100 m²/g
 25. The process according to claim 23, wherein the silica-basedparticles are present in a sol having an S-value in the range of from 8to 50%,
 26. The process according to claim 21, wherein the drainage andretention aids comprise cationic polymer and anionic clay of smectitetype.
 27. The process according to claim 21, wherein the drainage andretention aids comprise cationic and anionic organic polymers.
 28. Theprocess according to claim 21, wherein the cationic polymer is cationicstarch or cationic acrylamide-based polymer.
 29. The process accordingto claim 23, wherein the cationic polymer is cationic starch or cationicacrylamide-based polymer.
 30. The process according to claim 21, whereinthe cationic polymer contains one or more aromatic groups.
 31. Theprocess according to claim 21, wherein it further comprises adding tothe suspension one or more sizing agents.
 32. The process according toclaim 21, wherein the cellulosic suspension contains filler.
 33. Aprocess for the production of paper which comprises (i) providing anaqueous suspension containing cellulosic fibres, and optional filler;(ii) adding to the suspension a cationic clay having 3R₂ stacking, theclay being added in an amount of at least about 0.01% by weight,calculated as dry clay on dry suspension; (iii) adding to the suspensionat least one cationic polymer in an amount of at least about 0.001% byweight, based on dry suspension; (iv) adding to the suspension anionicsilica-based particles in an amount of at least about 0.001% by weight,based on dry suspension; and (v) dewatering the obtained suspension. 34.The process according to claim 33, wherein it further comprises addingto the suspension one or more sizing agents. 35.-40. (canceled)